Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
  • C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
  • C23C16/45502—Flow conditions in reaction chamber
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/24—Deposition of silicon only
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
  • C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
  • C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
  • C23C16/45563—Gas nozzles
  • C23C16/45572—Cooled nozzles
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
  • C23C16/458—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for supporting substrates in the reaction chamber
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/02104—Forming layers
  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02518—Deposited layers
  • H01L21/02521—Materials
  • H01L21/02524—Group 14 semiconducting materials
  • H01L21/02532—Silicon, silicon germanium, germanium
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/02104—Forming layers
  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02612—Formation types
  • H01L21/02617—Deposition types
  • H01L21/0262—Reduction or decomposition of gaseous compounds, e.g. CVD

Definitions

• the present invention relates generally to methods for chemical vapor deposition (CVD) of undoped and doped silicon, and more particularly to a method for CVD of undoped and doped silicon employing a novel combination of flow rate, temperature and pressure to achieve improved film properties at a high rate of deposition at low pressure.
• CVD chemical vapor deposition
• Amorphous, polycrystalline and epitaxial silicon are used in the manufacturing of semiconductor devices and deposited onto substrates (i.e. wafers) by chemical vapor deposition. Such processes are carried out in a variety of commercially available hot wall and cold wall reactors. Deposition is accomplished by placing a substrate in a vacuum chamber, heating the substrate and introducing silane or any similar precursor such as disilane, dichlorosilane , silicon tetrachloride and the like, with or without other gases. Deposition rates of approximately 30 to 200 angstroms per minute are achieved for low pressure processes (less than 1 Torr) as described in "Polycrystalline Silicon for Integrated Circuit Applications" (T.
• LPCVD vertical furnace low pressure chemical vapor deposition
• Silane or other " - similar precursor and a carrier gas such as hydrogen and a dopant gas such as phosphine enter the gas injection tube (or tubes) 18 from the gas inlet tube (or tubes) 20 through the chamber seal plate 12.
• the gases exit the process chamber through the seal plate 12 and out the exhaust port 24.
• a plurality of heater elements 26 are separately controlled and adjustable to compensate for the well-known depletion of the feed gas concentration as the gas flows from the gas injection tube 18 to the chamber exhaust port 24.
• This type of deposition system typically operates in the 200 mTorr to 500 mTorr range (200X 10 ⁇ 3 Torr to 500 X 10 "3 Torr) .
• FIG. 2 Another prior art reactor is illustrated in Fig. 2 and described in detail in U.S. Patent 5,108,792.
• a substrate 28 is placed on a rotating substrate carrier 30, enclosed in a vacuum tight chamber having an upper quartz dome 32 and a lower quartz dome 34 and associated chamber wall 36.
• the substrate 28 is heated by upper lamps 38 and lower lamps 40.
• Reactant gases are injected through gas input tube 42 and exhausted through exhaust tube 44.
• This reactor overcomes some of the limitations of the vertical furnace reactor of Fig. 1.
• the reactor can be operated at higher pressures than vertical LPCVD furnaces and does not have an injector tube and its associated problems.
• a preferred embodiment of the present invention includes a method of operating a CVD reactor having a high degree of temperature and gas flow uniformity, the method of operation providing a novel combination of wafer temperature, gas flow and chamber pressure.
• a wafer is placed in a vacuum chamber wherein a reactant gas flow is directed in parallel with the wafer via a plurality of temperature controlled gas injectors, at a selected velocity causing the deposition rate to be limited only by the rate of delivery of unreacted gas to the wafer surface and the rate of removal of reaction byproducts.
• the novel combination of process conditions moves the reaction at the wafer surface into the regime where the deposition rate exceeds the crystallization rate, resulting in very small crystal growth and therefore a very smooth polysilicon film with a surface roughness on the order of 5-7 n for films 2500 angstroms thick.
• the process is configured to operate below what is known as the "transition" temperature, at which level each layer of film is deposited in an amorphous form and then — crystallizes as the deposition proceeds because of the lower energy of the polycrystalline structure.
• the silicon film is crystalline near the interface between the deposited material and the wafer surface, and amorphous near the top surface of the deposited material, resulting in a much smoother surface than can be achieved with prior art commercial equipment.
• An advantage of the present invention is that it results in smoother deposited film surfaces.
• a further advantage of the present invention is that it provides a process resulting in improved uniformity in film deposition from batch to batch.
• a still further advantage of the present invention is that it provides a method resulting in higher rate deposition of silicon with improved film smoothness and reproducibility between batches.
• Fig. 1 illustrates a multiple wafer stack prior art reactor
• Fig. 2 illustrates a single wafer prior art reactor
• Fig. 3 is a flow chart illustrating the steps of the preferred embodiment of the present invention
• Fig. 4 shows a reactor that can be used to implement the method of the present invention
• Fig. 5 is a list of operating parameters according to the present invention
• Fig. 6 is a graph of deposition rate vs temperature
• Fig. 7 is a graph of deposition rate vs pressure
• Fig. 8 is a graph of deposition rate vs silane flow
• Fig. 9 is a plot showing film thickness variations for a number of wafers
• Fig. 10 is a plot showing the variation in thickness for each of a number of wafers, from an average value.
• the process begins by placing a wafer on a carrier in a deposition chamber 46, for deposition of polysilicon and/or amorphous silicon.
• the carrier is rotated (48) and heated (50) .
• the order of steps 48 and 50 is not significant in that the rotation is for the purpose of enhancing the uniformity of silicon deposition, and may be initiated any time prior to the injection of reactant gases and then maintained during the deposition.
• the wafer is preferably heated as uniformly as possible, with heat sources above, below and surrounding the edge of the wafer.
• the temperature to which the wafer is heated is preferably below a temperature known as the "transition" temperature, the preferred temperature range for silicon deposition being 500°C-700°C.
• the transition temperature will be more fully discussed in the following text of the specification.
• the process gas for silicon deposition is initiated (52) .
• the gas pressure in the chamber is maintained at a selected pressure less than 3 Torr but preferably less than 1 Torr, and the gas is preferably injected through a plurality of cooled injector nozzles with injection ports in close proximity to the wafer edge, the nozzles oriented so as to direct the flow parallel and close to the wafer surface.
• the gas is controlled to flow at a velocity in excess of 10 cm/second and preferably at least 50 to 100 cm/second across the wafer surface in a narrow space confined to the region from the wafer surface to a maxiumum space above the wafer of W to 1W .
• the velocity of the gas should be sufficient to reduce the gas residence time to less than 500 milliseconds and preferably less than 200 milliseconds.
• the gas is turned off and evacuated from the chamber, the rotation is stopped, and the wafer removed (54) .
• the results achievable with the method of the present invention as described above in reference to Fig. 3 represent a major improvement in silicon deposition.
• silicon deposition or silicon, etc. will be used in this disclosure as a generic term to include polysilicon, amorphous silicon, and silicon with doping material.
• previous systems achieved high rates of silicon deposition (1,000-3,000 A/minute) by running chambers at relatively high pressures, typically in excess of 10 Torr. Silicon deposition occurring at such high pressures has the disadvantage in that it can cause a gas phase reaction which can produce particulate contamination on the wafer.
• a major advantage of the present invention is that the method provides a very high deposition rate at very low chamber pressures, resulting in very smooth, uniform and consistent surfaces. With the method of the present invention, deposition rates of 3,000 A/minute are achieved at chamber pressures in the range of 300-700 mTorr.
• Film uniformity is typically 1%, measured between the center of a 200 mm diameter silicon wafer and a point 3 mm from the edge of the wafer.
• a wafer/ substrate is placed on a rotatable carrier in a vacuum chamber wherein a high velocity reactant gas for depositing silicon, such as silane, and a dopant gas if required, enter the reactor/chamber in relatively close proximity to the rotated, heated wafer.
• the gas is injected across the wafer at a velocity in excess of 10 cm/second and preferably 50 to 100 cm/second or more, and is confined to a very narrow region above the wafer so as to maximize the gas concentration at the wafer surface.
• the reactant gas is preferably confined to the region extending from the wafer surface to J_" , but no more than l ⁇ " above the wafer.
• the high velocity gas stream passing across the wafer surface has the effect of thinning what is known as a "boundary layer" immediately above the wafer.
• the boundary layer is a region wherein unwanted reaction by-products collect. This layer normally slows the rate of incidence of reactant gas, and thereby slows the rate of deposition.
• the high velocity gas stream of the present invention sweeps out the unwanted by- products, thinning the boundary layer, allowing a higher rate of desired reactant gas to reach the wafer surface, i.e., resulting in a further increase in the relative concentration of the desired reactant species and reduced incorporation of unwanted reaction by-products in the deposited film.
• the combination of elements of the method of the present invention are selected to achieve a more uniform, smooth film.
• the rapid gas flow described above in combination with a chamber pressure of about 260 mTorr and a process temperature about 650 °C changes the character of the deposition from that of the prior art, moving it into a regime where the reaction is occurring below what is known as a "transition" temperature where the deposition rate exceeds the crystallization rate, providing the benefit of an unusually small amount of crystal growth.
• the result is a very smooth polysilicon film with a surface roughness on the order of 5-7 nm for films 2,500 A thick.
• the nominal surface roughness using a conventional prior art method is - approximately 70 nm as noted in the book "Polycrystalline Silicon for Integrated Circuit Applications" by Ted Kamins , page 54.
• transition temperature The nature and background of the phenomenon known as the "transition" temperature will now be described in further detail, and how the method of the present invention provides— for operation in this region.
• CVD chemical vapor deposition
• the underlying silicon atoms are unlikely to continue rearranging after they have been covered by further layers of deposited silicon atoms. This is an undesirable result, causing a rough film surface.
• films deposited slightly below the transition temperature each layer of the film is deposited in an amorphous form and crystallizes as the deposition proceeds because of the lower energy of the polycrystalline structure.
• Nucleation of crystallites is most likely to occur by heterogeneous nucleation at the lower silicon-silicon dioxide interface. Crystallization of the amorphous silicon proceeds from these initial nuclei, with the crystalline region propagating upward into the film by solid-phase epitaxial growth. When the crystallization rate is less than the deposition rate, only the lower portion of the film (starting from the silicon- silicon dioxide interface) crystallizes during deposition, even though the crystallization process continues during the subsequent heating that occurs after the deposition is terminated by shutting off the silane flow.
• the silicon film can be crystalline near the interface and amorphous near the top surface resulting in a very smooth surface texture that is five to ten times smoother than the typical values obtained from conventional polysilicon deposited films carried out m presently available commercial equipment
• prior art equipment and methods do not allow such operation m a practical application because the deposition rate is very slow
• high deposition rates of 3,000 A/minute are only __ possible with chamber pressures above 10 Torr
• the method of the present invention provides a combination of elements, including rapid application of reactant gas and removal of unwanted by-products, reducing the boundary layer, operation between 500°C-700°C and at a pressure less than 3 Torr that results m operation below the transition temperature at a very high deposition rate m a range including 3,000 A/mmute.
• the non-uniformity of the deposited silicon layer is less than 1.5%, measured between the center of the wafer and a point 3mm from the edge of a 200 mm diameter wafer.
• the surface roughness is m the order of 5-7 nm for a film 2,500 A thick, deposited at a chamber pressure of 1 Torr or less .
• Fig 4 shows a reactor 56 having a rotatable susceptor 58 upon which is placed a wafer 60.
• a gas injector apparatus 62 including a plurality of nozzles with nets/openings 64, is positioned m close proximity to the wafer edge 66, and is oriented to direct a flow of reactant gas across and parallel to the wafer 60 The gas is further confined to a narrow region of width D above the wafer surface by a thermal plate 68 positioned over the wafer.
• the speed of gas flow from injector 62 across the wafer was found to optimally exceed 50 to 100 cm/second m the direction indicated by arrow 70, for the purposes of optimum reactant gas supply to the wafer __ surface and removal of reaction by-products according to the method described above.
• the substrate/wafer 60 is first placed on a carrier 58 and then brought to an operating temperature between 500 °C and 700 °C.
• the apparatus of Fig. 1 can reach the temperature m about 20 seconds.
• the apparatus as shown m Fig. 4 includes heaters 72 above, 74 below, and a heat block 76 surrounding the carrier. This combination provides uniform heating of the wafer 60.
• the carrier is then rotated at a speed of approximately 5 RPM, and the reactant gas is injected.
• the method of the present invention minimizes deposition on chamber surfaces by specifying that the reactant gas be confined to a narrow region above the substrate.
• Fig. 4 includes the plurality of water-cooled injector nozzles, prevention of reactant gas flow underneath the wafer, gas nozzles/jets __ directed across and positioned close to the ends of the wafer, and uniform wafer heating with heaters above, below, and around the edge of the wafer.
• Figs. 6-10 Various performance factors are illustrated in the graphs of Figs. 6-10.
• Fig. 6 shows the silicon deposition rate versus wafer temperature with a chamber pressure of 250 mTorr. It can be seen that the deposition rate is a rapid function of temperature at 250 mTorr and therefore fairly critical.
• Fig. 7 shows the deposition rate versus chamber pressure at a temperature of 650 °C.
• Fig. 6 shows the silicon deposition rate versus wafer temperature with a chamber pressure of 250 mTorr. It can be seen that the deposition rate is a rapid function of temperature at 250 mTorr and therefore fairly critical.
• Fig. 7 shows the deposition rate
• Fig. 8 shows the deposition rate as a function of silane flow, which is proportional to the gas velocity over the wafer.
• Fig. 9 is a plot of the deposition thickness variation within each wafer, for 25 wafers. The maximum film thickness variation as shown is approximately 2.9%, with an average variation around 1.5%.
• Fig. 10 shows the variation in average film deposition thickness from one wafer to another for 25 wafers. The maximum deviation from the average for the batch is about 2%.

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• 1999
  • 1999-09-15 JP JP2000570390A patent/JP2002525841A/ja active Pending
  • 1999-09-15 DE DE69936727T patent/DE69936727D1/de not_active Expired - Lifetime
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  • 1999-09-15 EP EP99949661A patent/EP1123423B1/de not_active Expired - Lifetime
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